784 



PHYSIOLOGY 



distinct relation between the amount of acid present in the gastric 

 contents and the opening of the pylorus. One may indeed say that 

 acidity of the gastric contents exercises a direct inhibitory stimulus 

 on the pyloric sphincter. 



These movements of the two portions of the stomach may be 

 observed also on anaesthetised animals and even on a stomach which 

 has been excised and placed in warm salt solution. They must 

 therefore have their origin in the walls of the stomach itself. Although 

 the co-ordination between the two parts of the stomach, between 



FIG. 336. Sketch of human stomach, in erect position, shortly after a 

 bismuth meal. (HERTZ.) 



F, fundus ; u, umbilicus ; IA, incisura angularis ; PC, pyloric canal ; 



o, oesophagus. 



the tonic contractions of the fundus and the rhythmic contractions 

 of the pyloric part, may be carried out by the local nervous system 

 Auerbach's plexus situated between the layers of the muscular 

 coat, it is probable that the advancing waves of contraction observed 

 in the antrum are myogenic, i.e. directly originated in and determined 

 by the muscle fibres themselves. We have no direct evidence that 

 these movements persist after throwing the local nervous system out 

 of action ; yet it is evident that they do not partake of the nature 

 of a true peristalsis, since they are not preceded by a wave of 

 relaxation. The opening of the pylorus, on the other hand, which 

 occurs at increasingly frequent intervals at the end of a wave, 



